1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display (LCD) configured to effectively prevent white coordinates from being yellowish.
2. Description of the Related Art
In the pursuit of larger screen televisions in recent years, flat panel display devices, such as liquid crystal display devices (LCDs), plasma display panels (PDPs), or organic electroluminescent display (OLED) devices, have been actively developed in place of cathode ray tubes (CRTs). In particular, much attention has been paid to LCDs because they are small, thin, and light in weight compared to the other flat panel display devices.
A typical LCD is constructed such that a liquid crystal material having an anisotropic dielectric constant is injected between an upper insulating substrate and a lower insulating substrate. Common electrodes and color filters are formed on the upper insulating substrate, while thin-film transistors and pixel electrodes are formed on the lower insulating substrate. In addition, the molecular arrangement of the liquid crystal material is changed by variations in the field strength of an electric field formed in the liquid crystal material. The strength of the electric field is controlled by generating different potentials between the pixel electrodes and the common electrodes. Accordingly, the amount of light transmitted to the upper insulating substrate is controlled to display desired images. For example, upon application of an electric field, the molecules of the liquid crystal material layer change their orientation to change the polarization of light passing through the liquid crystal material layer. Appropriately positioned polarizing filters selectively block the polarized light, creating dark areas that can represent desired images. A representative example of such an LCD includes a thin-film transistor liquid crystal display (TFT LCD) using a TFT as a switching device.
The color filters for representing color images are provided on either of the panels and an organic insulating layer covering the color filters. The organic insulating layer is usually thick enough to smooth the surface of the panels such that the field generating electrodes thereon have a uniform flat surface.
However, the thick or organic layer reduces the light transmittance especially for the blue light, thereby causing so called yellowish phenomenon. In other words the color sensation becomes yellowish.
In general, an LCD is formed of pixels each having three colors, for example, red, green, and blue. An LCD having a pixel structure of four colors has recently been developed by adding white pixels to the red, green, and blue pixels to improve luminance and resolution.
However, in the case of a LCD having a pixel structure with four colors, the area of the blue pixels is relatively smaller than the area of the red pixels and the green pixels. Thus, the amount of blue element is reduced in the blue pixel area, and white coordinates move toward red and green pixel areas. Accordingly, the white coordinates become yellowish. In order to prevent such a problem, blue elements are increased in a back- light of a transmissive LCD, and thus, the white coordinates are prevented from being yellowish.
However, a reflective LCD and a transflective LCD use an external light source, such as natural light or indoor light and do not use a separate back- light. Thus, the blue elements of the light source for the reflective LCD and the transflective LCD cannot be increased. In addition, a red color filter R.F, a green color filter G.F, and a blue color filter B.F of the conventional reflective LCD use a color photoresist having a high transmittance to minimize the reduction in luminance due to color filtering, thus maximizing the luminance. Thus, the red color filter R.F, the green color filter G.F, and the blue color filter B.F cannot sufficiently block other colors as shown in the graph of FIG. 1. In other words, the blue color filter B.F cannot sufficiently block a red beam and a green beam, and the red color filter R.F cannot sufficiently block a blue beam and a green beam. Further, the green color filter G.F cannot sufficiently block a blue beam and a red beam. Thus, saturation of the colors is deteriorated, and the color reproducibility of the LCD is lowered. Accordingly, the yellowish problem is more serious in the LCD having the pixels of four colors, wherein the area of the blue pixels is smaller than the area of the red pixels and the green pixels.